1. Field of the Invention
The present invention relates to a sliding contact and a method of producing the contact.
2. Description of the Related Art
A well-known type of a sliding contact of an encoder for used in what is called a mouse and the like is shown in FIGS. 10(a) and 10(b). Such a sliding contact has a support 2 for moving above a resistor 1 (a pulse switch substrate may be used instead of the resistor) in the direction indicated by the arrow. A relatively wide base 3 made of an elastic material is supported by the support 2. The leading end of the base 3 is extended toward the resistor 1, and connected to an abrasive-resistant precious metal contact 4 in contact with the resistor 1 by, for example, welding. The precious metal contact 4 is formed by fixing fine wires 4a, each having a folded portion in contact with the resistor 1 at its end and a portion in contact with the base 3 at its other end, onto a linear plate 4b by electric resistance welding.
FIGS. 10(c) and 10(d) show another type of sliding contact having a construction which is basically similar to that of the contact shown in FIG. 10(a). In this case, the portion in contact with the resistor 1 is specially devised in its shape.
However, the above sliding contacts of the prior art have the following problems:
(1) Since the precious metal contact 4 has, at its end, the folded portion in contact with the resistor 1 and the fine wires are arranged in a row, the processing of the contact 4 is troublesome.
(2) The precious metal contact 4 needs a sufficient contact area in order to prevent the contact portion from falling due to the pressure when the other end of the precious metal contact 4 abuts against the resistor 1 located in the extending direction of the base 3. The length of the base 3 is thereby shortened. The base 3 is made of an elastic material, and the shortening of the base 3 hinders free deformation of the base 3, thereby making the pressure of the precious metal contact 4 against the resistor 1 unstable and lowering reliability of the precious metal contact 4.
(3) Since the precious metal contact 4 is formed with wires, there are many useless portions except for the contact point, and thus the cost is high. Furthermore, although the precious metal contact 4 is given a function for stabilizing the pressure by being made of an elastic precious metal and lengthened in order to solve the problem (2), the material of the contact 4 is limited to specific precious metals, and the amount of the used precious metal is increased, thereby increasing the cost.
(4) Since the assembling of the precious metal contact 4 and the connection of the precious metal contact 4 and the base 3 are performed by welding, the welding process takes much time. Furthermore, since the precious metal contact 4 is formed with wires as described above, it is necessary to take special trouble in positioning the precious metal contact 4 during the welding process.